1. Field of the Invention
This invention relates to a tone generator system for synthesizing musical tones by using computer software, and a storage medium storing the computer software.
2. Prior Art
Conventionally, a tone generator system for synthesizing musical tones by using computer software has been proposed e.g. by U.S. Pat. No. 5,117,729, in which the sounding mechanism (physical phenomena) of a natural musical instrument is simulated for synthesis of musical tones having a tone color of the natural instrument. This type of tone generator system is called "physical model tone generator".
The physical model tone generator simulates the sounding mechanism of a natural musical instrument in the following manner:
If a natural musical instrument to be simulated is a wind instrument, a signal (excitation signal) representative of breath pressure of a player is generated, and a physical phenomenon occurring after the generation of the breath pressure and until the breath pressure passes through the instrument tube and turns into a musical tone signal is simulated at least by delaying and looping the excitation signal.
On the other hand, if the natural musical instrument to be simulated is a string instrument, a signal (excitation signal) is generated which is representative of an initial vibration of a string determined by the speed and pressure of bowing by the player, and a physical phenomenon occurring after the generation of the initial vibration and until the initial vibration causes vibration of the string and the vibration turns into a musical tone signal is simulated at least by delaying and looping the excitation signal.
The physical model tone generator that simulates the sounding mechanism of a natural musical instrument at least by delaying and looping an excitation signal as described above can be easily implemented by computer software. Actually, computer software programs implementing the physical model tone generator are commercially available.
However, in the conventional physical model tone generator, i.e. the physical model tone generator implemented by computer software, musical tones are generated almost only by computation. This requires the computer to execute a large amount of operation. Further, the amount of operation required increases with an increase in the number of musical tones generated simultaneously, imposing a heavy burden on a CPU of the computer even if the CPU has current improved performance. The amount of operation required is almost the same even when the physical model tone generator does not output any musical tone, i.e. when no tone is being generated. In other words, the CPU is under at least a certain level of computational load all the time during operation. As a result, when the physical model tone generator is started and when its processing is being executed, it can sometimes happen that other application programs cannot be started or executed even though no tone is being generated.
The above described problem of the computational load on the CPU also applies to software tone generators (i.e. tone generators for synthesizing musical tones by using computer software) other than the physical model tone generator, which also suffer from the above problem to a greater or lesser degree. To solve this problem, the present assignee has proposed a technique of reducing the computational load on a CPU employing a software tone generator of FM method type by Japanese Laid-Open Patent Publication (Kokai) No. 10-74088. According to this technique, an output waveform of a musical tone signal is signal monitored, and when its amplitude becomes smaller than a predetermined reference value, computation by a predetermined waveform generating block (block described by software) is stopped for reduction of the computational load on the CPU.
To reduce the computational load on the CPU when the physical model tone generator is employed as a software tone generator, one may consider simply applying the above technique for the software tone generator of FM method type to the physical model tone generator such that musical tone outputs are monitored and processing by the physical model tone generator is stopped when a no tone-generating condition is detected.
In the physical model tone generator, however, since a musical tone is generated at least by delaying and looping an excitation signal, as described above, there is a delay between a time point a command for sounding is issued and a time point a musical tone signal is output. Therefore, there can be a case in which a command for sounding is issued even when no tone is generated. In such a case, if the physical model tone generation processing is stopped based solely upon results of monitoring the output waveform of the musical tone signal, it would cause interruption of computation for tone-signal synthesis, resulting in that a musical tone intended by the player is not generated.